Electronic filters are used today to suppress noise, reject unwanted signals, or in some way manipulate the characteristics of an input signal. Typical semiconductor based filter designs comprise inductor, resistor and/or capacitor networks. Such networks are often placed together with separate transient voltage suppression (TVS) devices such as Zener diodes to provide ESD protection in addition to signal processing. The capacitance contribution of the TVS device often is used to further shape the filter characteristic.
An elliptic or Cauer filter is one type of filter design that utilizes inductors and capacitors. Elliptic filters are desirable in certain applications such as electromagnetic interference (EMI) or Universal Serial Bus (USB) filter applications, because they have equal ripple in both the pass band and stop band, a sharp cut-off characteristic, a low group delay for given stop-band characteristics, and excellent stop band attenuation compared to other classic filter designs such as Chebyshev filters.
One challenge semiconductor based filter designers face is providing an effective design in as small a space as possible in order to meet the size requirements that some applications demand. This challenge is often difficult, particularly when the filter design includes inductor and capacitor structures together with TVS devices.
Accordingly, a structure and method of manufacture are needed that improve the integration of passive components with TVS devices in order to meet the challenges described above as well as others.
For simplicity and clarity of illustration, elements in the figures are not necessarily to scale, and the same reference numbers in different figures denote the same elements. Additionally, descriptions and details of well-known steps and elements are omitted for simplicity of the description. As used herein, current carrying electrode means an element of a device that carries current through the device such as a source or a drain of an MOS transistor or an emitter or a collector of a bipolar transistor or a cathode or anode of a diode, and a control electrode means an element of the device that controls current through the device such as a gate of an MOS transistor or a base of a bipolar transistor. Although the devices are explained herein as certain N-channel or P-channel devices, a person of ordinary skill in the art will appreciate that complementary devices are also possible in accordance with the present invention. For clarity of the drawings, doped regions of device structures are illustrated as having generally straight line edges and precise angular corners. However, those skilled in the art understand that due to the diffusion and activation of dopants the edges of doped regions are generally not straight lines and the corners are not precise angles.